1. Field of the Invention
The present invention relates to a thermal type flowmeter for measuring flow rate with a heat-generating resistor being arranged in the fluid to be measured, more specifically, relates to measurement of the intake air flow rate and the exhaust gas flow rate of an internal combustion engine of an automobile.
2. Description of the Related Art
With respect to a flow rate sensor for detecting intake air volume of an internal combustion engine for an automobile and the like, a thermal type air flow rate sensor capable of direct measuring of mass flow amounts has been mainly in use.
In recent years, one wherein a sensor element of a thermal type flowmeter is manufactured using micro machine technology on a semiconductor substrate such as silicon (Si) has been proposed. In such a thermal type flowmeter of a semiconductor type, a heat generating resisting body is shaped in a thin film part of several microns shaped in the semiconductor substrate. As it is a thin film, the heat capacity is small, and a quick response and low power consumption are possible. Further, it is easy to shape construction by micro-fabrication to detect the temperature difference of the down-stream and the up-stream of the heat generating resisting body and to judge following current/reverse current.
With respect to the conventional technology of the thermal type flowmeter of the type described above, there is one described in the Patent Document 1.
(Patent Document 1) The Japanese Unexamined Patent Publication No. 2000-146652
For example, in detecting intake air flow rate of an internal combustion engine for an automobile, water droplets mixed in the intake air are attached to a flow rate detecting element and measuring error occurs. Particularly, in the thermal type flowmeter of a semiconductor type, because the detecting part is of a thin film, the heat capacity is small, therefore, if the water droplets are attached to the heat generating part, the temperature of a thin film part lowers sharply, and measuring of the flow rate may become impossible. Further, by attachment of the water droplets, the thin film part is cooled rapidly and the measuring element may possibly be destroyed.
In the conventional technology, flow rectifying blades are shaped integrally with a sensor element. If the water droplets fly in to the thermal type flowmeter of such construction, the water droplets are trapped by the rectifying blades once, crawl along the side face of a flow rectifying member by the wind pressure, and thereafter, may possibly separate from the flow rectifying blades and attach to the resistance body shaped region of the measuring element. In the conventional technology, the problem on attachment of water droplets has been left.